METABOLIC STRESS DURING WINTER INCREASES THE TOXICITY OF SELENIUM TO FISH

This study examined the effect of reductions in water temperature and photoperiod, mimicking winter conditions, on the toxicity of combined dietary (5.1 mug/g dry weight) and waterborne (4.8 mug/l) selenium to juvenile bluegill (Lepomis macrochirus). Elevated selenium caused hema tological changes and gill damage that reduced respiratory capacity, w hile increasing respiratory demand and oxygen consumption. Elevated se lenium in combination with low water temperature (4-degrees-C) caused reduced activity and feeding, depletion of 50-80% of body lipid, and s ignificant mortality within 60 days. Fish in warm-water selenium expos ures continued to actively feed and lipid depletion did not occur desp ite increased oxygen consumption. The combination of stress-related el evation in energy demand and reductions in feeding due to cold tempera ture and short photoperiod, leading to severe depletion of stored body lipid, is given the name Winter Stress Syndrome. This syndrome caused bluegill to undergo an energetic drain that resulted in death of abou t one-third of the fish. Results indicate that the current US national water quality criterion for selenium is not adequate to protect young bluegill and other species that substantially reduce activity and fee ding during cold weather. Aquatic contaminants should be evaluated in the context of seasonal metabolic changes that normally occur in test organisms. Winter Stress Syndrome could be an important, but as yet un quantified mortality factor in many circumstances.